This invention generally relates to using storage devices in virtualized environments.
With the increased use of software defined environments such as cloud computing and/or software defined datacenters, there is a need for efficient virtualization along all physical resources. The advantages of virtual machine technology have become widely recognized. Among these advantages is the ability to run multiple virtual machines on a single host platform. This can make better use of the capacity of the hardware, while still ensuring that each user enjoys the features of a “complete” computer. An additional benefit of virtualization, in some implementations, is greater security.
A virtual machine (VM) is a software abstraction, or “virtualization,” of an actual physical computer system. Multiple virtual machines (VMs) can be installed on a physical host machine, referred to as a “host,” which includes physical system hardware. The physical system hardware typically includes one or more physical processors and physical memory and various other physical devices, such as an input/output (IO) storage adapter to perform protocol conversions required to access a remote storage such as over a shared storage access network (SAN).
The virtual system hardware ordinarily includes one or more virtual processors, virtual memory, at least one virtual disk, and one or more virtual devices all of which may be implemented using software to configure physical components of a physical machine to emulate the virtual components. One or more layers of co-resident software components comprising a virtualization intermediary, e.g. a virtual machine monitor (VMM), hypervisor or some combination thereof acts to instantiate and provision VMs and to allocate host resources dynamically and transparently among the VMs so that their respective guest operating systems can run concurrently on a single physical machine.
Most all cloud computing environments heavily rely on virtualization of their resources. Well known are the technologies for central processing unit (CPU) virtualization, where many of the virtual machine concepts are now integrated into the processor architecture. Examples of these are dualities of page tables, interrupt routing, etc. This has significantly increased the performance of CPU virtualization and also contributed to the isolation properties among virtual machines that must be satisfied.
In contrast, storage I/O devices have seen limited attention for efficient sharing. In general, I/O devices are still managed indirectly by the hypervisor. Guest virtual machine interact through their device drivers to a virtual device that trapped into the hypervisor, where the storage function is then implemented against a storage device. In many cases, virtual disks (vdisks) are managed by the hypervisor as files. This leads to significant inefficiencies as disk I/O in the guest results in a trap into the hypervisor, where a full I/O stack then needs to be traversed to translate the block access to the vdisk to a file access request, ultimately leading to a block request on the real device.